All references cited herein are incorporated by reference into this application in their entirety.
Insulin and Insulin-like Growth Factors stimulate the growth of human breast cancer cells in vitro. The Insulin-like Growth Factors I (IGF-I) and II (IGF-II) interact with cell surface receptors eliciting their cellular response. The IGF-I receptor (IGF-R) is the cell surface receptor for IGF-I having high binding affinity for this growth factor. However, IGF-R is also thought to have a high binding affinity for IGF-II. Interaction of either of these two growth factors to the IGF-R elicits intracellular responses through protein tyrosine phosphorylations, which can be blocked through the inhibition of the interaction of either IGF-I or IGF-II to the receptor.
These intracellular responses of IGF-IR signaling are implicated in the inducement of cell growth, proliferation and anti-apoptosis. It has been shown that the IGF-IR can not only induce normal cell growth but also induces tumor cell growth in both breast cancer and prostate cancer. In addition, the anti-apoptotic activity of IGF-IR protects cancerous tumor cells from chemotherapeutic treatments in breast cancers.
Therefore, a need exists for a method of inhibiting IGF-IR in order to inhibit tumor cell growth and increase sensitivity to chemotherapeutic agents. The activity of the IGF-IR can be inhibited by various methods. One of these methods comprises inhibiting the activation of the IGF-IR by preventing binding of agonist such as IGF-I or IGF-II. This can be achieved by blocking the IGF-IR binding site with antagonists.
Antibodies can be effective antagonists in inhibiting the interaction of the IGF-IR with IGF-I or IGF-II. αIR-3 (Arteaga, C. L. and Osborne, C. K.; Cancer Research 49, 6237-6241, 1989) is an antibody with high affinity for the IGF-IR and has been found to inhibit the interaction of IGF-I with the IGF-IR. In in vitro experimentation this murine antibody has been found to inhibit the growth of various tumor cells from breast cancer cell lines. In various tumor cells (MCF-7, MDA-231, ZR75-1, and HS578T) this αIR-3 could inhibit the IGF-I mediated DNA synthesis in vitro. However, in estrogen dependent tumor cells, such as MCF-7, ZR75-1 and T47D, the inhibition with αIR-3 of the IGF-IR in vivo failed to block estrogen stimulated DNA synthesis or proliferation. In contrast, in T61 tumor cells the αIR-3 antibody could inhibit tumor cell growth in vivo when used in combination with down-regulation of IGF-II synthesis by simultaneous treatment with estradiol and tamoxifen. It appears that αIR-3 is a better antagonist for IGF-I blockage compared to its ability to inhibit interaction of IGF-II with IGF-IR.
Another murine antibody against the α-subunit of IGF-IR, 1H7 (Li S. et al; Biochemical and Biophysical Research Communications, 196, 92-98, 1993), has shown good results in inhibiting the activation of IGF-IR. In in vitro experimentation with NIH3T3 cells over-expressing human IGF-IR the 1H7 antibody inhibits basal, IGF-I or IGF-II stimulated DNA synthesis. A second antibody raised against the IGF-IR α-subunit, 2C8, however, is unable to block IGF-IR activation by either IGF-I or IGF-II while having binding affinities for the receptor.
While these two murine antibodies, αIR-3 and 1H7, have shown results in inactivation of the IGF-IR in vitro, their ability to inhibit estrogen dependent tumor cell growth in vivo is limited. Furthermore, the monoclonal murine antibodies have their obvious disadvantages in their use for human treatment or other mammals. In addition, their relative complexity limits the ability to manipulate the antibodies to optimize their use in the treatment of mammalian hormone dependent cancers. Accordingly, improvements are sought.